Lock units customarily used for side-doors of motor vehicles utilize a latching mechanism, known as a catch, which receives a catch-bolt, or striker, disposed on a pillar of the vehicle doorframe. The catch is biased to an open position wherein a slot of the latch housing is aligned with a recess of the catch. As the door is shut, the striker enters the recess through the slot and rotates the catch to a closed position in which the striker is retained in the recess by a pawl which prevents the catch from rotating toward the open position. Typically the pawl is heavily biased towards the catch with the interface of the two comprised of a further negative biased angle to resist high acceleration forces. The latch housing is typically made of plastic and may be closed sealingly all-around by a cover outside the region of the slot. Such lock units typically include at least one release lever (e.g., an inside or outside door handle) and a displaceable locking mechanism (e.g., a lock cylinder at or in the outside door handle or a slide button disposed inside the window pane area of the door). In such a case, with the locking mechanism unlocked, the motion of the inside or outside door handle is interconnected through the mechanism and the motion separates the connection of the pawl and the catch by overcoming the pawl bias forces, thereby allowing the spring-loaded catch to move to the open position.
As required by law, lock units for doors, hatches and tailgates of motor vehicles must be provided with a secondary latched position in addition to the primary latched position. This secondary latched position falls between the primary latched position and the open position such that if the catch fails to reach the primary latched position, the door will be retained shut in the secondary latched position rather than moving all the way to the open position, which would obviously be dangerous to an occupant of a moving vehicle. In addition to preventing the vehicle door from opening during travel, the secondary latched position is also perceptible when a user does not close the vehicle door with sufficient force. By law, the secondary latched position leaves the door visibly ajar when the vehicle door is closed with too little force to be noticed that it is not securely latched. By applying additional force (e.g., leaning against the vehicle door), the latching mechanism can be forced into the primary latched position and the door completely shut.
When released from the primary latched position by actuating the release lever, the pawl abruptly breaks away from the corresponding locking surface of the catch and the spring-loaded catch moves at a high velocity to the open position. The abrupt movement of the locking surfaces against one another results in a significant opening clack followed immediately by a second significant clack caused by the catch making impact with a limit stop as it reaches the open position. Owing to the high forces biasing the locking surfaces of the pawl and catch against one another (and also biasing the catch toward the limit stop), the noises caused by opening the vehicle door are quite loud. Additionally, the high impacts on the pawl and catch can cause damage to the lock unit and severely limit its useful life, especially since most of the impact occurs along the locking surfaces.
German Patent Application No. DE 10 2007 003 948 A1 describes a multi-pawl latching mechanism which reduces both the latching noises during opening and the forces required to actuate the latching mechanism. The locking surfaces of the catch and a first pawl are correspondingly chamfered and canted to achieve a smooth and gradual sliding when the locking surfaces are released from one another. Because the locking surfaces were designed to reduce the resultant shear forces caused by the locking surfaces pressing against one another while the catch is released, the forces required to actuate the locking mechanism are also correspondingly reduced. Further, due to the reduction in forces acting on the latching mechanism, the noise produced during opening is significantly reduced.
However, because the locking surfaces are designed to slide relatively easily with respect to one another, the latching mechanism is not self-latching (i.e., the locking surfaces do not hold the catch in place on their own) and requires a pawl blocking lever to hold the first pawl against the catch in the primary latched position. Additionally, to achieve a secondary latched position, a second pawl is also required. To prevent the pawl blocking lever from engaging in the secondary latched position during closing, the second pawl is disposed in a separate plane from the catch, the first pawl and the blocking lever. The secondary latched position is achieved if the primary latched position fails to engage (e.g., first pawl slides off the catch) by a bolt extending from the catch to the plane of the second pawl which abuts a blocking arm of the second pawl in the opening path of the catch. Providing the second pawl on a different plane and the introduction of the bolt into the catch can be costly from a manufacturing standpoint, however. Thus, while the multi-pawl design effectively reduces opening noise and latch actuation forces, it requires multiple different components at multiple planes of the latching mechanism, thereby making the device relatively complex and expensive to manufacture.